Abstract
The CG-2 beamline at the High Flux Isotope Reactor (HFIR) exhibits a notable discrepancy between observed count rates and the count rates we would expect based on a Monte-Carlo neutron ray-trace simulation. These simulations consistently predict count rates approximately five times greater than those observed in four separate experimental runs involving different instrument configurations. This discrepancy suggests that certain factors are causing losses in measurements that are not adequately accounted for in the simulation, in particular guide reflectivity or misalignment. To investigate these discrepancies, a high-dimensional simulation parameter approach is applied in order to understand the losses. Region of Interest (ROI) groups along the instrument are assigned to different surfaces of the guide components within the simulation. This allows the parameters of those guide components to be varied as a group to minimize the complexity of the search space. The result is an optimization of simulation parameters using an iterative scheme that aims to minimize the difference between experimentally measured count rates and simulated count rates across all tested collimator combinations. This proposed methodology holds the potential to reveal previously unrecognized sources of intensity loss in the CG-2 beamline at HFIR and improve the accuracy of simulations, leading to enhanced understanding and performance of the beamline for various scientific applications.
| Original language | English |
|---|---|
| Article number | 169965 |
| Journal | Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment |
| Volume | 1069 |
| DOIs | |
| State | Published - Dec 2024 |
Funding
We would like to thank Lee Robertson for his initial work on the CG2 McStas simulation [22] and Ken Littrell for his help with an internal technical review of this work. A very special thanks to Thomas Huegle for both his initial work with Lee, as well as a detailed internal technical review of this work. This research was supported in part by an appointment to the Oak Ridge National Laboratory Undergraduate Research Student Internship, sponsored by the U.S. Department of Energy and administered by the Oak Ridge Institute for Science and Education. This research used birthright cloud resources of the Compute and Data Environment for Science (CADES) at the Oak Ridge National Laboratory, which is supported by the Office of Science of the U.S. Department of Energy under Contract No. DE-AC05-00OR22725. This research used resources at the High Flux Isotope Reactor, a DoE Office of Science User Facility operated by the Oak Ridge National Laboratory.
Keywords
- GP-SANS
- High Flux Isotope Reactor
- McStas
- Neutron guides